A tire mold usually consists of multiple tread segments that together form a full circular tread mold. The mold is closed on the side by a side ring, which typically has the tire brand engraving, and other information such as size and operating pressure. The tire mold tread segment surface is shaped to be the negative of the actual tire tread surface. The tire tread mold segments and the 2 side rings, are held together by a container.
The tire mold segments can include vent structures to selectively evacuate air from the tire mold. Various methods for air evacuation have been described, with high manufacturing complexity and maintenance efforts such as cleaning or replacement.
U.S. Pat. No. 4,812,281 discloses vent holes, having a diameter between 3.81 to 12.7 mm, to allow air to be evacuated through such holes that fluidly connect the mold inner surface to the mold outer surface.
U.S. Pat. No. 6,923,629 describes spring vents, which can close the vent structure once the tire green has complete filled up the tread pattern in the mold. During the rubber vulcanization process, air can escape through the vent holes, with the spring loaded pins stopping the rubber material from entering the vent holes. Spring vents can be costly, for example, can contribute up to 10% of the manufacturing cost of the mold.
U.S. Pat. Nos. 6,382,943 and 6,826,819 describe a ventless approach in which the tread pattern surface of the mold is built up by many small pitches, also referred to as puzzle elements. Air is evacuated by leaving a small gap between such puzzle elements. The gap is chosen in such way that the air can pass through while at the same time the rubber is held back during the curing process. The ventless process can be limited to simple tread pattern. For example, winter tires can have a too complex tread pattern to be built as a puzzle. Further, puzzle mold can incur high manufacturing cost, which can be up to twice as expensive as a regular segmented mold.
Patents EP2719524 and DE102012104500 describes micro-venting channels, which connect the tread mold surface to an evacuation cavity such as a hole on the rear side of the mold. The channels are narrow enough to hold back the rubber during the curing process, while at the same time, allowing air to be evacuated. As each slot can require a connection to a venting cavity, several thousand of such evacuation cavities can be required for venting of a complex tread pattern.
U.S. Pat. No. 8,834,143 describes mechanical inserts to create narrow slots for air venting. This can result in several thousand inserts for a complex tread design such as for a winter tire. Tight tolerance of both the slots and the inserts can be required, for example, to avoid ejection upon de-molding of the cured tire.
Thus there is a need for improved systems and methods for curing tires.